In the field of digital radiography a wide variety of image acquisition techniques have been developed rendering a digital representation of a radiographic image.
Among such techniques are computerised tomography, nuclear magnetic resonance, ultrasound detection, detection of a radiation image by means of a CCD sensor or a video camera, radiographic film scanning etc.
In still another technique a radiation image, for example an xray image of an object, is stored in a screen comprising a photostimulable phosphor such as one of the phosphors described in European patent publication 503 702 published on 16.09.92. The technique for reading out the stored radiation image consists of scanning the screen with stimulating radiation, such as laser light of the appropriate wavelength, detecting the light emitted upon stimulation and converting the emitted light into an electric representation for example by means of a photomultiplier and finally digitizing the signal.
One of the benefits of a digital radiographic system resides in the possibility of processing the digital image representation before display or hard copy recording. The term "processing" in this context means any kind of image-processing such as noise filtering, contrast enhancement, data compression etc.
The processing can be performed on-line or off-line, the present invention specifically relates to off-line processing on a graphical work station.
The procedure commonly followed on a workstation is as follows. The image signal acquired by an image acquisition device as described above is stored in memory and retrieved from that memory at the time of off-line processing, the actual processing is then performed and the processed image is applied to a monitor for display and evaluation. The processing takes into account processing parameters that are either associated to the image in the very beginning of the process, so for example in an image identification phase proceeding the read-out phase in case of a radiation image stored in a photostimulable phosphor screen. Alternatively processing parameters can be entered by the operator via the console of the work station or preset processing procedures can be applied. Processing on a work station is frequently performed interactively. Then the original image signal is processed during successive processing cycles with different parameter settings and is each time evaluated and reprocessed until the obtained result meets the objectives as to image quality or diagnostic requirement.
A digital radiographic image is commonly represented by about 10 MB digital data. The computation time required for processing such a amount of data may extend to orders of minutes per processing cycle.
In case of interactive processing, comprising multiple processing cycles, the display of successively processed images (with different processing settings) is each time interrupted by a relatively long wait cycle and the total processing procedure (depending on the number of interactive processing cycles) may be very long.